<?php
//include ("./index.php");
?>
<form name="login" method="post" action="./check_user.php">
<table align="center">
    <tr><td style="height:80px;"></td></tr>
    <tr>
        <td style="font-weight:bold;">Login</td>
    </tr>
    <tr>
        <td align="center">ID</td>
        <td style="height:50px;"><input type="text" name="id" style="width:300px;"></td>
    </tr>
    <tr>
        <td align="center">Password</td>
        <td style="height:50px;"><input type="password" name="pass" style="width:300px;"></td>
        <td><input type="button" value="login" onClick="check_user();"></td>
    </tr>
</table>
</form>
<script>

function check_user()
{

    var loginform = document.login;

    if(loginform.id.value == ""){
        alert("Please, enter your email.");
        return false;
    }

    if(loginform.pass.value == ""){
        alert("Please, enter your password.");
        return false;
    }

    loginform.submit();

}
</script>